Thermoplastic elastomers (TPEs) are a class of polymers that combine the properties of two classes of polymers, namely thermoplastics, which can be reformed upon heating, and elastomers, which are rubber-like polymers. One form of TPE is a block copolymer, containing some blocks whose polymer properties usually resemble those of thermoplastics, and some blocks whose properties usually resemble those of elastomers. Those blocks whose properties resemble thermoplastics are often referred to as “hard” segments, while those blocks whose properties resemble elastomers are often referred to as “soft” segments. It is believed that the hard segments provide properties similar to those provided by chemical crosslinks in traditional thermosetting elastomers, while the soft segments provide rubber-like properties.
In addition to the nature of the hard and soft segments, the weight and mole ratios of hard to soft segments determine to a great extent the properties of a TPE. For example, longer soft segments usually lead to TPEs having lower initial tensile modulus, while a higher proportion of hard segments leads to polymers with higher initial tensile modulus. Other properties can be affected as well. Thus, manipulation on the molecular level affects changes in the properties of TPEs, and improved TPEs are desired.
Frequently the soft segments of TPEs are formed from poly(alkylene oxide) segments. Heretofore the principal poly(alkylene oxides) have been based on polymers derived from cyclic ethers such as ethylene oxide, 1,2-propylene oxide and tetrahydrofuran, which are readily available from commercial sources. When subjected to ring opening polymerization, the cyclic ethers form the polyether glycols polyethylene ether glycol (PEG), poly(1,2-propylene ether) glycol (PPG), and polytetramethylene ether glycol (PO4G, also referred to as PTMEG), respectively.
TPEs derived from polytrimethylene ether glycol soft segments (also referred to as PO3G) and trimethylene ester, for example, polytrimethylene ether trimethylene terephthalate (PO3G/3GT), have been developed and used to make fibers. U.S. Pat. No. 6,599,625 discloses that fibers made of PO3G/3GT had a higher unload power and a lower stress decay than did comparable fibers made of polytetramethylene ether glycol (PO4G) soft segments and 3GT hard segments. However, the percent set was slightly higher for the PO3G/3GT fibers than for the PO4G/3GT fibers. Tenacity and elongation at break were not significantly different between the two types of fibers.
TPEs comprising soft segments of polytrimethylene ether ester and hard segments of tetramethylene ester, for example, polytrimethylene ether tetramethylene terephthalate (PO3G/4GT) are disclosed, for example, in U.S. Pat. No. 6,562,457, which discloses fibers prepared from such TPEs, and methods for spinning the fibers. The PO3G/4GT fibers are disclosed to have a higher unload power, lower stress decay, higher elongation, and lower percent set than did comparable fibers made of PO4G/4GT. With the exception of tenacity, most of the properties, such as the stress decay, elongation, unload power and set were comparable to those of the PO3G/3GT fibers for which data were reported in the '625 patent mentioned hereinabove.
Although elastomeric fibers having desirable physical properties are now available, a need remains for other articles, such as films, having similarly advantageous properties. Such films can be useful in making bags and packaging, e.g., for food, storage and transportation.